Would you aspirate a knee with suspected prepatellar bursitis?

Management of Suspected Prepatellar Bursitis

Aspiration is recommended for suspected prepatellar bursitis when infection is suspected to guide appropriate treatment and improve outcomes. 1

Diagnostic Approach

Clinical Assessment for Septic vs. Non-Septic Bursitis

• Evaluate for signs of infection:
  • Fever
  • Extensive surrounding erythema/cellulitis
  • Significant warmth
  • Severe pain
  • History of trauma with skin break
  • Immunocompromised status

When to Aspirate

• Aspiration is indicated when:
  • Infection is suspected (septic bursitis)
  • Diagnosis is uncertain
  • Significant fluid collection causing pain or limiting function

When Not to Aspirate

• Aspiration should be avoided in:
  • Clearly non-infectious chronic microtraumatic bursitis (occupational)
  • Minimal fluid collection with no signs of infection
  • Recent antibiotic use (may cause false-negative cultures)

Aspiration Procedure

• Use sterile technique, preferably with ultrasound or fluoroscopic guidance 2
• Obtain fluid for:
  • Cell count with differential
  • Gram stain
  • Crystal analysis (to rule out gout)
  • Aerobic and anaerobic cultures
  • Glucose measurement

Interpretation of Results

• Synovial fluid WBC ≥50,000 cells/mm³ with >60% neutrophils suggests septic bursitis 3
• Positive Gram stain has high specificity but limited sensitivity 3
• Positive culture is definitive for septic bursitis (found in ~80% of cases) 3

Management Based on Aspiration Results

Septic Bursitis (Positive Culture)

• Antibiotic therapy (initially targeting Staphylococcus aureus)
• Consider surgical drainage for:
  • Failure to respond to antibiotics
  • Recurrent cases
  • Extensive infection

Suspected Septic Bursitis (Negative Culture)

• If high clinical suspicion remains despite negative culture:
  • Consider repeat aspiration
  • Discontinue antibiotics for at least 2 weeks before re-aspiration if possible 2
  • Weekly repeat aspirations may be needed if clinical suspicion remains high 2

Non-Septic Bursitis

• Conservative management:
  • Ice, elevation, rest, analgesics
  • Address underlying cause (e.g., avoid kneeling)
  • Aspiration generally not recommended due to risk of iatrogenic infection 1

Important Considerations

• Patients on antibiotics prior to aspiration may have false-negative cultures 2
• Treatment duration should be at least 14 days, as shorter courses are associated with higher failure rates 4
• Bursal aspiration of non-infectious microtraumatic bursitis carries risk of iatrogenic septic bursitis and is generally not recommended 1
• Chronic bursitis may persist despite appropriate treatment, particularly in patients with occupational kneeling requirements 5

Follow-up

• Close monitoring for clinical improvement
• Consider repeat aspiration if:
  • No improvement after 48-72 hours
  • Worsening symptoms
  • CRP >10 mg/L despite initial treatment 3